# Constraints on the flux of $\sim (10^{16} - 10^{17.5})$ eV cosmic photons from the EAS-MSU muon data

## TL;DR

This paper reanalyzes EAS-MSU data to search for cosmic-ray photons in the energy range of 10^{16} to 10^{17.5} eV, setting new upper limits on gamma-ray flux and refuting earlier excess claims.

## Contribution

It provides the most stringent upper limits on gamma-ray flux at around 10^{17} eV using modern simulations and reanalysis of existing data.

## Key findings

- No confirmation of previous gamma-ray excess signals.
- Established the most restrictive flux upper limits at ~10^{17} eV.
- Refuted earlier indications of gamma-ray candidate excess.

## Abstract

Results of the search for $\sim (10^{16} - 10^{17.5})$ eV primary cosmic-ray photons with the data of the Moscow State University (MSU) Extensive Air Shower (EAS) array are reported. The full-scale reanalysis of the data with modern simulations of the installation does not confirm previous indications of the excess of gamma-ray candidate events. Upper limits on the corresponding gamma-ray flux are presented. The limits are the most stringent published ones at energies $\sim 10^{17}$ eV.